Near infrared spectroscopy of the DIII-D divertor*

A high speed, high resolution near infrared (NIR) spectrometer has been installed at \hbox{DIII-D} to make first-of-its-kind observations of the $0.8-2.2$~$\mu$m region in a tokamak divertor. The goals of this diagnostic are (1) to study Paschen spectra for line-averaged measurement of low temperature plasma parameters, (2) to benchmark the chemical and physically sputtered sources of neutral carbon using the lineshape of the CI, 910~nm multiplet, and (3) to quantify contamination of the 0.75$-$1.1~$\mu$m region where Thomson-shifted laser light is measured by the Thomson scattering diagnostic. Diagnostic capabilities include a 300~mm, $f/3.9$ design, 300$-$2400~Gr/mm gratings providing optical resolution of $\sim$0.65$-$0.04~nm, and readout at up to 900 frames/second. Data are presented in \hbox{L-mode} plasmas, and in \hbox{H-mode} between ELMs and during the ELM peak. Results acquired by this diagnostic will be applied to design of a proposed divertor Thomson diagnostic for \hbox{NSTX-U} and aid validation of the Thomson system on ITER.